Crude petroleum oil, and the heavier hydrocarbon fractions and/or distillates obtained therefrom, generally contain nitrogenous and sulfurous compounds in large quantities. In addition, crude oil, and the heavier hydrocarbon fractions contain quantities of metallic contaminants which exert detrimental effects upon the catalyst utilized in various processes to which the crude oil or heavy hydrocarbon fraction is ultimately subjected. The most common metallic contaminants are nickel and vanadium, although other metals including iron, copper, etc., are often present. These metals may occur in a variety of forms; they may exist as metal oxides or as sulfides, introduced into the crude oil as metallic scale or particles; in the form of soluble salts of such metals; usually, however, they exist in the form of organo-metallic compounds such as metal porphyrins and the derivatives thereof.
Although the metallic contaminants existing as oxide or sulfide scale may be removed, at least in part, by a relatively simple filtering technique, and the water-soluble salts are at least in part removable by washing and subsequent dehydration, a much more severe treatment is generally required to remove the organo-metallic compounds, and to the degree required in order that the resulting crude oil or heavy hydrocarbon fraction is suitable for further processing. In addition to the organometallic compounds, including metal porphyrins, crude oils contain greater quantities of sulfurous and nitrogenous compounds that are found in light hydrocarbon fractions such as gasoline, kerosene, light gas oil, etc. For example, a Wyoming sour crude, having a gravity of 23.2.degree.API at 60.degree. F., contains about 2.8% by weight of sulfur and about 2700 p.p.m. of total nitrogen. The nitrogenous and sulfurous compounds are converted, upon being subjected to a treating process, into hydrocarbons, ammonia, and hydrogen sulfide, the latter being readily removed from the system in a gaseous phase. Reduction in the concentration of the metallic contaminants is not as easily achieved, and to the extent that the crude oil or heavy hydrocarbon charge stock becomes suitable for further processing. Notwithstanding that the concentration of these compounds, such as metal porphyrins, is relatively small, for example, less than about 10 p.p.m., calculated as the elemental metal, subsequent processing techniques will be adversely affected thereby. For example, when a hydrocarbon charge stock containing metals in excess of about 3.0 p.p.m., is subjected to a cracking process for the purpose of producing lower-boiling components, the metals become deposited upon the catalyst employed, steadily increasing in quantity until such time as the composition of the catalytic composite is changed to the extent that undesirable results are obtained. That is to say, the composition of the catalytic composite, which is closely controlled with respect to the nature of the charge stock being processed and to the desired product quality and quantity, is changed considerably as the result of the deposition of the metallic contaminants onto the catalyst, the changed composite resulting in changed catalytic characteristics. Such an effect is undersirable with respect to the cracking process, since the deposition of metallic contaminants upon the catalyst tends to result in a lesser quantity of valuable liquid product, and large amounts of hydrogen and coke, the latter producing relatively rapid catalyst deactivation. The presence of organic metal compounds, including metal porphyrins, affects deleteriously other processes including catallytic reforming, isomerization, hydrodealkylation, etc.
In addition to the foregoing described contaminating influences, crude oils and other heavier hydrocarbon fractions, generally contain large quantities of pentane-insoluble material. For example, the Wyoming sour crude consists of about 8.37% by weight of pentane-insoluble asphaltenes which are hydrocarbonaceous compounds considered as coke-precursors having the tendency to become immediately deposited within the reaction zone and onto the catalytic composite employed in the form of a gummy hydrocarbonaceous residue. This constitutes a large loss of charge stock; it is economically desirable to convert such asphaltenes into useful hydrocarbon oil fractions.
The object of the present invention is to provide a much more efficient process for hydrorefining heavier hydrocarbonaceous material and particularly petroleum crude oils, utilizing a catalyst prepared in a particular manner. As hereinabove set forth, the prior art has removed metals by deposition of the same on the catalyst employed. This greatly increases the amount of catalyst in a very short time, and precludes the use of a fixed-bed catalyst system. Slurry processes, employing catalytically active metals deposited upon silica and/or alumina, are extremely erosive, and make plant maintenance difficult and expensive.